To the synthetic organic or polymer chemist, simple methods for forming carbon-carbon bonds are extremely important and valuable tools. One method of C—C bond formation that has proved particularly useful is transition-metal catalyzed olefin metathesis. “Olefin metathesis,” as is understood in the art, refers to the metal-catalyzed redistribution of carbon-carbon bonds. See Trnka and Grubbs (2001) Acc. Chem. Res. 34:18-29. Over two decades of intensive research effort has culminated in the discovery of well-defined transition metal alkylidene complexes that are highly active olefin metathesis catalysts and stable in the presence of a variety of functional groups.
Examples of these transition metal alkylidene complexes are described in U.S. Pat. Nos. 5,312,940, 5,342,909, 5,831,108, 5,969,170, 6,111,121, and 6,211,391 to Grubbs et al., assigned to the California Institute of Technology. The complexes disclosed in these patents all possess metal centers that are formally in the +2 oxidation state, have an electron count of 16, and are penta-coordinated. These catalysts are of the general formula XX′M(LL′)=CRR′ wherein M is a Group 8 transition metal such as ruthenium or osmium, X and X′ are anionic ligands, L and L′ are neutral electron donors, and R and R′ are specific substituents, e.g., one may be H and the other may be a substituted or unsubstituted hydrocarbyl group such as phenyl or C═C(CH3)2. Such complexes have been disclosed as useful in catalyzing a variety of olefin metathesis reactions, including ring-opening metathesis polymerization (“ROMP”), ring closing metathesis (“RCM”), acyclic diene metathesis polymerization (“ADMET”), ring-opening metathesis (“ROM”), and cross-metathesis (“CM” or “XMET”) reactions.
Such metathesis catalysts include those that have been prepared with phosphine ligands, e.g., triphenylphosphine or dimethylphenylphospine, exemplified by phenylmethylene-bis(tricyclohexylphosphine)ruthenium dichloride

wherein “Cy” is cyclohexyl. See U.S. Pat. No. 5,917,071 to Grubbs et al. and Trnka and Grubbs (2001), cited supra. These compounds are highly reactive catalysts useful for catalyzing a variety of olefin metathesis reactions, and are tolerant of many different functional groups. See Schwab et al. (1995) Angew. Chem, Int. Ed. Engl. 34:2039-2041 and Schwab et al. (1996) J. Am. Chem. Soc. 118:100-110. However, as has been recognized by those in the field, the compounds display low thermal stability, decomposing at relatively low temperatures. Jafarpour and Nolan (2000) Organometallics 19(11):2055-2057.
More recently, significant interest has focused on such transition metal alkylidene catalysts wherein one of the phosphine ligands is replaced with an N-heterocyclic carbene ligand. See, e.g., Trnka and Grubbs, supra; Bourissou et al. (2000) Chem. Rev. 100:39-91; Scholl et al. (1999) Tetrahedron Lett. 40:2247-2250; Scholl et al. (1999) Organic Lett. 1(6):953-956; and Huang et al. (1999) J. Am. Chem. Soc. 121:2674-2678. N-heterocyclic carbene ligands offer many advantages, including readily tunable steric bulk, vastly increased electron donor character, compatibility with a variety of metal species, and improved thermal stability. See Scholl et al. (1999) Tetrahedron Lett. 40:2247-2250; Scholl et al. (1999) Org. Lett. 1:953-956; Chatterjee et al. (2000) J. Am. Chem. Soc. 122:3783-3784; and Bielawski et al. (2000) Angew. Chem. Int. Ed. 39:2903-2906, A representative of these second generation catalysts is the ruthenium complex (IMesH2)(PCy3)(Cl)2Ru═CHPh

wherein Cy is cyclohexyl, Ph is phenyl, and Mes represents mesityl (2,4,6-trimethylphenyl).
These transition metal carbene complexes have been found to address a number of previously unsolved problems in olefin metathesis reactions, particularly cross-metathesis reactions. However, metathesis reactions with directly functionalized olefins, particularly olefins that are directly substituted with an electron-withdrawing substituent, remain a formidable challenge.
For example, acrylonitriles are unusually difficult substrates to use in olefin metathesis reactions, and only one single-component catalyst system, based on molybdenum, has been described as active for cyano-olefin cross-metathesis (Crowe et al. (1995) J. Am. Chem. Soc. 117:5162-5163; Brümmer et al. (1997) Chem. Eur. J. 3:441-446). This is in part due to the fact that these olefins are directly substituted with an electron-withdrawing group, and in part a result of the metal-coordinating ability of the cyano group. See Randl et al. (2001) Synlett, pp. 430-432, Blanco et al. (1999) Synlett, pp. 557-558, Gessler et al. (2000) Tetrahedron Lett. 41:9973-9976, and Cossy et al. (2001) J. Organomet. Chem. 634:216-221.
Accordingly, there is a need in the art for an effective and efficient method of carrying out an olefin metathesis reaction using olefins substituted with an electron-withdrawing group, e.g., a cyano-substituted olefin.